Hello everyone!

I recently experimented with a 40W fluorescent tube, and because I didn't have a suitable ballast at hand, I used a 20W ballast.
Now I've realized that I like the slightly lower light output for the fixture in my living room.

Is it bad for the tube when it's permanently run on a ballast that is too small?

Some info:
- I'm using a 6V heating transformer parallel to the lamp.
- The ballast is for 18/20/23/24/26W TL/TLC lamps.
- When fully on, the heating voltage across the filament is at 3.2/3.4 volts.
- The ballast gets hand warm at best.
- The tube is a Sylvania 40W warm white black ender with normal electrodes.

Probably OK down to about 1/2 of the rated current even without extra cathode heating. Can be down to zero if some adequate cathode heating is constantly applied. Get yourself a dimmable electronic ballast to play. 1-10V versions can be controlled with just a simple 47-100K variable resistor across the input terminals, and most of DALI versions can be also controlled by applying 230V to DALI terminals through a pushbutton (check with a ballast datasheet).


Also, it is said to allow new lamp to run the first 100 hours at full power before attempting to dim, to complete electrode activation to form.

Okay thanks

I would also recommend using a different tube, that Sylvania tube you describe is extremely old and rare, Sylvania only used black end caps on T12 tubes until the mid 1950's by then they switched to aluminium end caps

so thats very much a tube that should be preserved and not used, I would love to see a picture of it on the gallery if your able to post one



also such an old tube will have 9V high resistance cathodes, so needs more voltage to keep the cathodes warm, your current system however would be much better suited for a Rapid-start specification tube, any tube with RS or Rapid start in its etch, for example a TL RS or TL-M RS